The use of ceramic components in internal combustion engines has increased as engine manufacturers have discovered that the ceramic materials used for these components resist wear and have other desirable characteristics not possessed by the conventionally used metals. The use of ceramic materials can produce a dramatic reduction in wear when used to form engine components. Not only do ceramic engine components exhibit outstanding wear characteristics, but they also display high strength and are capable of withstanding thermal shock and corrosive environments. Moreover, these desirable characteristics are retained at the high temperatures and stresses typically encountered during internal combustion engine operation. The contact stresses to which a ceramic engine component can be subjected often approach 250,000 psi.
Structures including ceramic link elements proposed for use in internal combustion engines are the ball and socket joints of the fuel injector drive train and cylinder drive train components disclosed in U.S. Pat. No. 4,806,040 and the ceramic tipped pivot rods disclosed in U.S. Pat. Nos. 4,794,894 and 4,848,286. These patents, however, are not directed to longitudinal rod- or shaft-shaped link elements formed completely of ceramics, but are primarily concerned with the dimensional parameters of and tensile stresses on the ceramic parts of structures described therein. Moreover, they do not specifically address the improvement of mechanical strength and reliability of the ceramic elements.
U.S. Pat. No. 4,629,707 discloses a high strength ceramic element that can have a shaft configuration. However, the ceramic material from which this element is made is a low mass ceramic with an open porosity, the degree of which determines the strength of the element. A shaft made from the ceramic described in this patent is not likely to withstand the high compressive loads to which it would be subjected in a heavy duty diesel engine.
The formation of strong, reliable link structures useful in an internal combustion engine from ceramic materials is difficult. When a ceramic tip is mounted at the end of a metal element to produce the link, a specially configured mounting portion, such as those disclosed in U.S. Pat. Nos. 4,794,894 and 4,848,286, must be formed. Not only are such arrangements cumbersome and costly, but the bonding reliability between the ceramic and the metal tends to be low. In addition, wear resistance of the ceramic element may be unacceptable.
To avoid the problems associated with a combination ceramic-metal link, it has been proposed to form the link entirely of ceramic material. If the ceramic link must contact a metal surface during engine operation, both the contact surface and the shaft of the ceramic link must have sufficient mechanical strength to resist wear and continue to function for an acceptable period of time in a typical engine operating environment. Even if the ceramic link is an integral element made from a silicon nitride sintered body under predetermined manufacturing conditions, the mechanical strength of the shaft and the durability of the contact surfaces may vary from link to link. Therefore, a highly reliable ceramic link cannot be produced unless it is possible to reproduce the optimum mechanical and durability characteristics of the link during the manufacturing process.
The prior art fails to disclose a ceramic link element having a shaft integrally formed with spherical contact surfaces that may be manufactured in a way that provides reproducible optimum strength and durability. A need exists, therefore, for an integral ceramic link element for an internal combustion engine that may be manufactured to conform to acceptable strength and reliability parameters at low cost.